Silica/elastomer composites and method of producing same

ABSTRACT

A silica/elastomer composite produced by reacting an ethylene or propylene containing copolymer having units   WITH A SILICA SUBSTRATE BY HYDROLYSIS OF THE SILANE GROUP, AND THEN POLYMERIZING THE ALLYL GROUP TO AN ELASTOMER.

Elite States Patent Wiggill [54] SILICA/ELASTOMER COMPOSITES AND METHODOF PRODUCING SAME [72] Inventor: John B. Wiggill, Orange, Tex.

[73] Assignee: E. I. du Pont de Nemours and Company,

Wilmington, Del.

[22] Filed: Sept. 17, 1969 [21] Appl. N0.: 858,879

[52] US. Cl ..ll7/62.l,117/45,1l7/72, 117/118,117/123 D, 117/124 F,117/126 GS, 117/126GN,117/161ZA Primary Examiner-William D. MartinAssistant Examiner-D. Cohen A!t0rneyEarl L. Handley Mar. 14, 1972 [57]ABSTRACT A silica/elastomer composite produced by reacting an ethyleneor propylene containing copolymer having units t2h9,,

I cm,

and units such as with a silica substrate by hydrolysis of the silanegroup, and then polymerizing the ally] group to an elastomer.

5 Claims, No Drawings SILlCA/ELASTOMER COMPOSITES AND METHOD OFPRODUCING SAME formula (A):

I l T and units having the formula (B):

l l C|C,

I c =o l E I F with a silica substrate and then polymerizing the pendantunsaturated F group to an elastomer.

it is known in the art to produce copolymers of ethylene or propylenecontaining units having the formula (A):

1 40. T. R T

and radicals having the formula:

I C,C|

where G is a carbon atom in the main polymer chain, Y is a radicalselected from the class consisting of 0- and N l R Q is a divalentradical having one to 22 carbon atoms that is bonded through carbonatoms to both Y and T, T is a silicon containing radical selected fromthe class consisting of l I I S|iand S|iO Si v v N I M where N is one to28, M is 1; Z is a hydrolyzable group; R is a radical selected from theclass consisting of hydrogen and hydrocarbon containing radicalscontaining one to 22 carbon atoms; V is selected from the classconsisting of R and Z, and X is halogen. Such copolymers are disclosedand claimed in 7 U.S. Pat. No. 3,408,420. It is further disclosed insaid patent that the halogen atom can be reacted with a hydroxyl group,carboxylic acid group or NH group-containing substrates or with othermonomer units to further modify the polymer properties."

It is also known in the art, to react an alpha olefin copolymercontaining unit having the formula:

with one or more different monomers having groups that react with acidhalide, such as allyl alcohol to produce a copolymer capable of furtherreaction. Such copolymers are disclosed in British Pat. No. 1,064,026.

The present invention employs as one starting material the copolymer ofU.S. Pat. No. 3,408,420, in which the unreacted groups are reacted withan unsaturated alcohol, an unsaturated amine, or an unsaturatedmercaptan. The alcohol, amine, or mercaptan may contain from three to 40carbon atoms. Thus, the compound reacting with the acid halidecontaining polymer may have the formula:

D E F wherein Dis HO, ll-lN or SH, E is a divalent radical having one to22 carbon atoms that is bonded through carbon atoms to both D and F, andF is a radical having the formula:

and R is hydrogen or a hydrocarbon radical having one to 22 carbonatoms. Specific compounds having this formula that are satisfactory are:allyl alcohol; 5 hexen-l-ol; allyl mercaptan; p-allyl phenol; 3buten-l-ol; 4 penten-l-ol; 3 methyl-3 buten-l-ol; 2 methyl-2propen-l-ol; O-allyl phenol; l-allyl cyclohexanol; 4-hexen-l-ol; hydroxystyrene; amino styrene; diallyl amine; 3 hexen-l-ol; 7-octen-l-ol; 6hepten-l-ol; and

' allyl amine.

The reaction of the unsaturated molecule with the copolymer containingthe silane group may be carried out while the copolymer is dissolved insolution. As disclosed in U.S. Pat. No. 3,408,420, a solution ofcopolymer containing the silane group is obtained as this copolymer isformed, that is the copolymer is formed by dissolving an alphaolefin/acid halide copolymer and then reacting some or all of the halidegroups with a silane compound such asgamma-amino-propyltriethoxy-silane. if less than a stoichiometric amountof the silane compound is added to the solution, acid halide groupsremain. The unsaturated compound may then be added to react with theseremaining acid halide groups. in the I copolymer used to react with theglass and the elastomer, the

number of units having the formula (A):

(where D is a D radical that has lost one hydrogen atom reaction withthe acid halide, i.e., O,-S or will be present in amounts of between 0.1and 24.9 mol percent of the total units in the copolymer. The totalnumber of units A and B should normally not exceed 25 mol percent of theunits in the copolymer.

The copolymer is normally applied to the silica surface from a solutionof the copolymer in a suitable solvent and as carbon tetrachloride,tetrachloroethylene, trichloroethylene, toluene, benzene, xylene,cyclohexane, hexane, and the like. The copolymer is preferably presentin the solvent to the extent of between about 0.1 and 50 parts per 100parts by weight solvent. The reaction of the copolymer and the silicicsurface takes place on contacting the silicic surface with the solutionof the copolymer. The hydrolysis reaction forms a linkage which in thegeneral formula (A) above would correspond to where Si is a silicon atomof the silicic surface. Silicic surfaces normally absorb water from air,but even dried silicic surfaces cause reactions to take place. Coatingsilicic substrates with copolymer of this type is disclosed in US. Pat.No. 3,427,18 7,

issued Feb. 11, 1969. The copolyrner may also be applied as aaccomplished by sulfur curing, then the elastomer must containunsaturation such as is present in natural rubbers, and rubbers formedfrom dienes. A particularly useful class of elastomers are those formedby coordination polymerization of ethylene-propylene, and hexadiene-l,4.If the bonding of the rubber is to be accomplished by a peroxide cure,the elastomer need not contain unsaturation, and the elastomers may be,for example, an ethylene/propylene copolymer or chlorosulfonatedpolyethylene. Thus the F radical of formula (B) above is polymerized tothe elastomer through the valences shown as unfilled in the followingformula pendant from the divalent E radical The silicic substrate coatedwith the copolymer may be combined with the elastomer to form thecomposite of this invention by many techniques, which will differsignificantly depending on the type of final article desired. If it isdesired that the final article he a tight glass to rubber seal, asaround the windows of a vehicle, the uncrosslinked rubber would beapplied to the edge of the silicic substrate, and then cured. If on theother hand the final article is to be a reinforced elastomeric article,the glass would be in the form of fibers which could be fed to anextruder along with the elastomer. Likewise, ifthe final article is tobe a rubber tire having a belt of glass fiber under the tread, the beltmight be applied over the cord and then the uncrosslinked rubberapplied.

It is therefore apparent that the amount of glass and the amount ofelastomer in the final article will vary with the particular articlebeing made. in the case of molded articles containing glass fiber forreinforcement, the amount of glass fiber will usually be between 5 and50 percent by weight of the total.

Normally the curing agent is added to the elastomer as it is added to ormixed with the silicic substrate. The amount of curing agent added isnot substantially more than that needed to cross-link the elastomer;about 3 to 10 weight percent the elastomer is conveniently used. Theagents and combination of agents used to cross-link elastomers may beused. Thus, one or more peroxide initiators or one or more sulfurcompounds may be used.

The temperatures at which the curing of the silicic/elastomer compositeis accomplished are those conventional in the elastomer curing art, andmay vary from 50 C. to 200 C.

ln the following examples which illustrate the invention all parts andpercents are by weight.

EXAMPLE 1 A random ethylene-methacrylic acid copolymer, whosecomposition was 87.8 weight percent ethylene units and 12.2 weightpercent acid units, was completely converted to the acid chloridederivative using phosphorous pentachloride; an infrared scan of a filmpressed from the ethylene-methacrylyl chloride polymer had a peak at 5.6microns due to the acid chloride carbonyl and no peaks at 3.0, 6.1 and6.6 microns. Ten grams of this ethylene-methacrylyl chloride polymerwere dissolved in 500 cc. of tetrachloroethylene with heating andstirring at C. When the polymer was completely in solution 1.46 cc. ofgamma-amino-propyl-triethoxy-silane were added to react with thepolymer. The mixture was stirred briefly and 0.73 cc. of S-hexen-l-olwas added with continued stirring.

The solution thus prepared was used to coat glass fibers of about 0.5inch length which were added to the solution, and then strained out.

Ten weight percent of the thus coated glass fibers were mixed with anethylene/propylene/ 1,4-hexadiene terpolymer (90 weight percent)containing about 67 mol percent ethylene, 31 mol percent propylene, and1-2 mol percent hexadiene, by milling on a Farrell Birmingham rubbermill having 3-inch rollers. One roller was operated at 37 r.p.m. and theother roller at 26.4 r.p.m. at a temperature of C. A curing agentconsisting of 5 parts of ZnO; 1.5 parts of tetramethylthiurammonosulfide; 1.5 parts of sulfur; and 0.75 part of 2-rnercaptobenzothiazole was added, and the mixture milled for 15 minutes.

The composition was then molded into a sheet 6 X 6 X 0.05 inches on apress at 40,000 lbs. pressure at 160 C. for 2 minutes, and held at thatpressure and temperature for 45 minutes.

The molded sheets were then die cut to proper testing shape. The tensileand flexural specimens were cut at a 90 angle at opposite ends of thecompression molded sheet. The specimens were tested for tensile strengthASTM D-638, elongations at break ASTM D638, and stiffness ASTM D-747;the results (average of 4 determinations) are shown (as item 1) in Tablel, which also shows the results (average of 4 determinations) obtainedon the same cured elastomer without the glass fibers, item 2, the samecured elastomer containing 10 weight percent glass fibers but withouttreatment of the glass fibers with a coupling agent, item 3, the samecured elastomer containing 10 weight percent glass fibers having acoating of the coupling agent obtained by reacting a stoichiometricamount of garnma-aminopropyl-triethoxysilane with the ethylenemethacrylyl chloride polymer, item 4.

tained 17.6 weight percent acid chloride. This copolymer was reactedwith 0.6 equivalent of the silane of Example 1, and 0.4 equivalent ofallyl amine. The glass to be coated was quickly passed through the flameofa Meker Burner, and after cooling to room temperature, dipped into thesolution and dried. The glass was then heated in an oven at 100 C. for 1hour.

The elastomers were formed into 6 inch X 6 inch X 0.020 inch sheets bymeans of a press operated at 50 C. for 1 minute at 100 p.s.i. Thesesheets were cut into 1 inch X 6 inch strips and a sandwich of the glass,elastomer and polyethylene terephthalate was made. The elastomer to betested was covered on the side opposite the glass with a sheet 6?polyethylene terephthalate.

The sandwich was then cured in a press at p.s.i. After curing, theelastomer with the polyethylene terephthalate still in place wasstripped from the glass using an lnstron equipped with rubber facegrips, at a crosshead speed of 2 inches/minute.

Table 11 gives the results.

TABLE II Coupling Cure Cure agent recipe cycle Peal (0.03% (defined(defined strength Elustomer Form on glass) below) below) (lbs/inch)Natural Rubber:

(Smoked Crepe). Gurn Stock. None 0 Do.... ..do.... Yes 0.35 Do.... BlackFilled Yes 0.85

Styrene/Butadiene:

6.0 10.1 9.1 3.0 oil extended. D0 ..do Yes B B 3.9Ethylene/Propylene/Hexadienez Nordel 1040 C... C 004 Do C... C.. 0.56Do. C... C.. 1.2 Do..... C C... 4.2

Vrstalon 3509 C C... 0.05 Do. C. C... 1.7 Do. Black Filled C C 5.1

Royalene 301 Gum Stock C C 0.06

Do C C 3.7 Do. C C... 0.14 Do... C... C 10.7

Chlorosulfonated Polyethylene Hypalon D.... D... 0.4

Do... D D... 10.2 D... D 20.9

*Copolymer of ethylene/methacrylyl chloride containing 17.6 weightpercent acid chloride units reacted with a stoichiometric amountofgamma-amino-propyl-triethoxy silane.

g but no B units.

EXAMPLE 2 A group of commercially available elastomers were bonded toglass strips to test the adhesion of the elastomer to the glass.

The copolymer coupling agent was prepared as in Example 1, except thatthe ethylene/methacrylyl chloride copolymer con- Definitions: "curerecipeused in Ta le II (pans per hundred parts resin Zinc Oxide 6.0Sulfur 3.5 Stearic acid 1.0

Cure recipe: A

Same as A. but additionally 30 parts of high abrasion furnace black areadded. Cure recipe: B

Zinc Oxide 5.0 Sulfur 2.0 Stcaric acid 1.5

Cure recipe: B

Zinc Oxide 5.0 Sulfur 2.0

Mercaplobcnzothyiozyldisulfide 2.75 Cure recipe: C

Zinc Oxide 5.0 Tetramethyl thiuram monosulfide l.5 Mercaptobenzothiazole0.75 Sulfur L Cure recipe: C

Same as C. but also containing 30 arts of high abrasion furnace black.Cure reci e: D

Sublimated Litharge 2.5 Mercaptobenzothyiazyldisulfide 0.5Dipentumelhylenethiuram tetrasulfidc 2.0 Definitions: cure cycle used in Table ll Cure Cycle A: 145' C. for IS minutes Cure Cycle B: 145 C. for50 minutes Cure Cycle C: I6U C for minutes Cure Cycle D: I45 C. for 30minutes EXAMPLE 3 Approximately the same results may be obtained using acoupling agent formed by the reaction of ethylene/methacrylyl chloridecopolymer containing 17.6 weight percent acid chloride, that has beenreacted with 0.7 equivalent of gamma aminopropyl triethoxy silane and0.3 equivalent ofallyl alcohol.

I claim:

1. A process for producing silica/elastomer composites which comprisesreacting a solution of a copolymer containing at least 50 mol percentalpha olefin units of two to three carbon atoms, and at least 0.1 to24.9 mol percent units of the formula (A):

where C is a carbon atom in the main copolymer chain Y' is selected fromthe class consisting of oxygen and Q is a divalent radical having one to22 carbon atoms that is bonded through carbon atoms to both Y and T, Tis a silicon containing radical selected from the class consisting of Eis a divalent radical having one to 22 carbon atoms that is bondedthrough carbon atoms to both D and F, and F is a radical having theformula H -c=c R R the total number of units (A) plus (B) being presentin the copolymer in amounts not in excess of 25 mol percent, with asilica substrate. by hydrolyzing at least some of the Z groups while thesolution of the copolymer is in contact with a silica substrate to forma coating on at least a portion of the silica substrate, intimatelycontacting the thus coated silica substrate with an elastomer andpolymerizing said elastomer to the coating on the silica substratethrough the pendant unsaturated group F of the units of formula B.

2. A composite comprising silica tightly bound to an elastomer through acopolymer containing at least 50 mol percent alpha-olefln units of twoto three carbon atoms and at least 0.1 to 24.9 mol percent units of theformula (A) and at least 0.1 to 24.9 mol percent units of the formula(B) l i l Q is a divalent radical having one to 22 carbon atoms that isbonded through carbon atoms to both Y and T, T is a silicon containingradical selected from the class consisting of Y -Si and where N is l to28 and M is l, R is a radical selected from the class consisting ofhydrogen and hydrocarbon containing radicals containing one to 22 carbonatoms, V is selected from the class consisting of R and Z, Z is ahydrolyzable group, D is oxygen, sulfur, or

E is a divalent radical having one to 22 carbon atoms that is bondedthrough carbon atoms to both D and the group, Si is a silicon atom inthe silica substrate, and the valences of the group pendant from thedivalent E radical shown in formula (B) as unfilled, are polymerized toan elastomer, the total number of units (A) plus (B) being 5. Theprocess of claim 1 in which D is E is -Cl-l and F is

2. A composite comprising silica tightly bound to an elastomer through acopolymer containing at least 50 mol percent alpha-olefin units of twoto three carbon atoms and at least 0.1 to 24.9 mol percent units of theformula (A)
 3. The process of claim 1 in which the elastomer containspendant unsaturation, and in which the polymerizing of the elastomer tothe coating is by means of a sulfur containing cross-linking agent. 4.The process of claim 1 in which D'' is oxygen, E is -CH2- and F is 5.The process of claim 1 in which D'' is E is -CH2- and F is